Modern industrial systems often employ closed-loop feedback to provide accurate process control. Such closed-loop systems require accurate sensing of the parameters to be controlled. In the case of rotary position (or motion), magnetic resolvers are a preferred sensing means. A common magnetic resolver employs a rotor mounted on a rotating shaft which is magnetically coupled to a stator positioned closely adjacent the rotor. Excitation of a coil on the rotor will produce a magnetic field. The magnetic flux lines of this field, which rotates with the rotor, are sensed by first and second stator coils. The sinusoidal currents induced in these sense coils by the rotor coil's magnetic flux is representative of the rotor's rotational position.
If digital position data is desired rather than these analog signals, the sinusoidal position signals can be fed into a resolver-to-digital converter to produce digital position information. Known resolver-to-digital converters have been designed to directly accept these sinusoidal outputs of the known resolver to produce binary outputs.
This known resolver, however, has a major drawback in the complexity of both its rotor and stator windings. Multiple coils are required on both the rotor and the stator. Therefore, multipole resolvers can become extremely intricate and, as a result, costly to manufacture. It has been shown that the rotor of a resolver can be greatly simplified by replacing the rotor coil windings with permanent magnets. The permanent magnets act to change the reluctance seen by the flux of the stator sense coils when those coils are excited. U.S. Pat. Nos. 4,604,575 and 4,764,767 are representative of such permanent magnet resolvers. These known devices, however, utilize complex output circuits in order to produce digital position information. It is an object of the present invention to overcome this and other problems of known resolvers.